Many hormones and neurotransmitters regulate biogenic functions through specific receptors present in cell membranes. Most such receptors transmit intracellular signals through the activity of coupled guanine nucleotide-binding proteins (G proteins). These receptors have a common structure with a 7 transmembrane region, and are thus referred to as G protein-coupled receptors or seven transmembrane receptors (7TMR).
Examples of such G protein-coupled receptor proteins include human receptor protein encoded by phGR3 (or GPR10) gene (Genomics, 29:335 (1995)) and its corresponding rat receptor protein UHR-1 (Biochem. Biophy. Res. Commun.) 209: 606 (1995)).
PrRP (Nature, 393:272–276 (1998)) is known as a physiologically active peptide that functions as a ligand for the aforementioned phGR3 and UHR-1.
PrRP has been found to have prolactin-releasing action specific to anterior pituitary hormone in in vitro pituitary cell culture systems (Nature, 393:272–276 (1998)), but other types of physiological action, particularly the effects on posterior pituitary hormone, remain unclear. The endogenous regulatory hormone that regulates oxytocin, a posterior pituitary hormone, is currently unknown.